1. Field of the Invention
The present invention relates to an electronic product equipped with a heat radiating plate, and more particularly relates to an electronic product wherein an electronic component, including a high power transistor, is mounted on and adhered to a heat radiating plate, and is encapsulated in an enveloper.
2. Description of the Related Art
In general, a high power transistor, such as a power MOSFET or the like, which is frequently utilized in an analog amplifier or the like, generates a large amount of heat in operation. Thus, when an electronic component includes the high power transistor, an electronic product which uses the electronic component including the high power transistor, is equipped with a heat radiating plate made of a suitable metal material, such as copper or the like, to thereby facilitate radiation of heat from the electronic component.
The electronic product is provided with an enveloper for encapsulating the electronic component, to protect the electronic component from the outside, and leads of the electronic component pass and extend through the enveloper. When the enveloper is made of a suitable thermosetting resin, the electronic product is called a resin-sealed package. Also, when the enveloper is made of a suitable ceramic material, the electronic product is called a suitable ceramic package. Further, when the enveloper is made of a suitable metal material, the electronic product is called a metal package.
Conventionally, the electronic product of resin-sealed package type including, for example, the power MOSFET, is manufactured as explained below.
The electronic component is mounted on and adhered to the heat radiating plate, such that electrode pads of the electronic component, provided on a bottom face thereof, are electrically connected to the heat radiating plate. Also, the electronic component has two sets of electrode pads provided on a top face thereof, and the respective sets of electrode pads are connected to inner lead sections of two leads through bonding-wires. Thereafter, the electronic component and the inner lead sections are put in a molding cavity of a metal mold, and then sealing-resin is injected into the molding cavity, whereby the electronic component and the inner lead sections are enclosed with and encapsulated in the molded resin, with outer lead sections of the leads being protruded from the molded resin. Thus, in the conventional resin-sealed package, the electronic component and the inner lead sections are in direct contact with the molded resin.
When electric power consumption of the high power transistor is too large, it generates a very large amount of heat during an operation of the electronic component, SO that the molded resin may be subjected to deterioration and exfoliation. In this case, the characteristics of the electronic products are changed, resulting in a decline in the operational reliability.
Also, as stated above, since the molded resin is in direct contact with the electronic component and the inner lead sections, it may serve as a dielectric layer, resulting in production of a parasitic capacitance. Accordingly, due to the interference based on the production of the parasitic capacitance, the frequency characteristics of the electronic product may be deteriorated in a high-frequency band of more than 1 GHz. In particular, the deterioration of the high-frequency characteristics causes serious problems in microwave applications of the electronic product.
In manufacturing the electronic product of ceramic or metal package type, the electronic component is mounted on and adhered to the heat radiating plate, such that the bottom electrode pads of the electronic component are electrically connected to the heat radiating plate. Then, a rectangular ceramic or metal frame member is securely attached to the heat radiating plate such that the electronic component is encompassed by the ceramic or metal frame. Thereafter, the respective two leads are put on tops of opposing side walls of the ceramic or metal frame, and the respective sets of top electrode pads are connected to the inner lead sections of the two leads through bonding-wires. After the electrical connections of the sets of top electrode pads to the inner lead sections of the lead are finished, a ceramic or metal lid member is securely adhered to the top opening end of the ceramic or metal frame, thereby forming the ceramic or metal package for accommodating and sealing the electronic component, with the outer lead sections of the leads being protruded from the interface between the frame member and the lid member.
The electronic product of ceramic or metal package type not be subjected to the aforesaid problems involved in the resin-sealed package. However, it is impossible to obtain the inherent advantages derived from the resin-sealed package, as stated below.
Historically, the ceramic or metal package has been used in a high-power transistor, such as the power MOSFET or the like, for obtaining a high operational reliability. However, it is desirable to realize an electronic product, including the high-power transistor, as a resin-sealed package, which can be manufactured with a high productivity at low cost.
Certainly, according to the ceramic or metal package, it is possible to obtain a higher operational reliability and a higher operational performance, in comparison with the resin-sealed package. Nevertheless, the manufacturing cost of the ceramic or metal package, including the cost of materials, is higher than that of the resin-sealed package.
Especially, before an operational reliability of the electronic product of ceramic package type can be enhanced, it is necessary to eliminate thermal stresses, resulting from variations in temperature, from the ceramic package as much as possible. To suppress the production of thermal stresses in the ceramic package, thermal expansion coefficients of materials for manufacturing must be matched with that of the ceramic enveloper. Nevertheless, the scope of choice of the materials for manufacturing the ceramic package is considerably restricted, because there are not many kinds of materials having thermal expansion coefficients which can be matched with that of the ceramic enveloper. Also, for metal materials, having thermal expansion coefficients which can be matched with that of the ceramic enveloper, although there are tungsten/copper alloy, molybdenum/copper alloy or the like, these metal materials are relatively expensive.
Accordingly, if the electronic product, which should be conventionally manufactured as a ceramic or metal package, is constituted as a resin-sealed package, it could be expected that the manufacturing cost of the electronic product can be considerably lowered.